To protect life, code mandates the use of egress emergency lighting in commercial, institutional, and industrial buildings. Egress lighting design considerations account for the area of space to be lighted, the occupant load in the space, and the shortest distance of travel between occupants and nearest legal exit doors. Placement of overhead egress lighting, therefore, is over main non-obstructed circulation paths. Egress luminaries are available as stand-alone units or incorporated into ambient lighting luminaries and have functionality limited to providing lighting.
Code mandates that in the event of power interruption, auxiliary emergency power illuminates the egress path. The auxiliary power may be located in overhead luminaries employing batteries, or a remote location employing inverters or generators. However, maintaining short-lived batteries and lamps at high and often difficult to reach places can be costly. Further, the failure rate is unpredictable, requiring unscheduled maintenance to comply with code requirements. Current lamp technology requiring large and heavy inverters is inefficient and typically requires provisions for venting, making the implementation costly. The alternative to the inverter is the use of the generator, however, a generator must be placed outside the building on a specially constructed pad and screening, creates noise while operating, requires special exhaust methods. The generator is more costly and there is also an increased risk of theft.